1. Field of the Invention:
This invention relates generally to material removal, and more specifically to an apparatus and method for electrochemically smoothing or finishing an irregular surface of a conductive metal part.
2. Description of the prior art:
Electrochemical finishing or smoothing of conductive metal parts is a well-known process in which irregular metal surfaces such as burred metal surfaces or the like, are removed from a conductive metal part. In the process, a stationary conductive metal part (anode) is connected to the positive post of a rectifier, and a separate stationary conductive metal part (cathode) mounted adjacent the anode is connected to the negative post of the rectifier. A face of the cathode is mounted adjacent the anode surface to be finished to define a gap therebetween, which is filled with an electrolyte fluid. The irregular anode surface or burr is electrochemically dissolved or removed by anodic action, that is, by current flow from the anode surface through the electrolyte to the face of the cathode. In this known process, any contact between the stationary anode surface and stationary cathode face must be avoided to prevent an electrical short circuit therebetween which may damage the anode or cathode. Therefore, to prevent contact, the gap between the anode surface and the cathode face is maintained at about 0.020 inch (0.051 cm) to accomodate the irregular width of the burrs which are inconsistent.
During the electrochemical process, the burr is removed along with some adjacent anode metal, resulting in a rounded corner surface as shown for example by the dotted line in FIG. 1. Assuming a gap of 0.020 inch (0.051 cm) and a burr of 0.040 inch (0.102 cm), for a total total incremental distance of 0.060 inch (0.153 cm), the removal rate of anode metal to the removal rate of the burr is equal to the ratio of the gap to the total incremental distance, or a ratio of 1:3. Accordingly, removal of the burr will result in the removal of adjacent anode metal of about 0.013 inch (0.033 cm). This presents a problem in that too much metal is removed from anode surface, which can deleteriously affect the strength characteristics of the part by decreasing the thickness of the wall at the corner. This problem can be overcome in the prior art by masking the corner adjacent to the burr with insulating material to prevent electrochemical dissolution of the metal at the corner, resulting in a square corner. However, masking the corner surfaces is a difficult and time consuming process, particularly where the anode surface is in a hard-to-get at location.
An electrochemical grinding machine is also known in the art comprising a rotatable diamond wheel made of electrically conductive metal to which diamond chips are secured at the periphery thereof. The wheel forms a cathode connected to the negative terminal of a power rectifier. A fixed metal part to be ground by the diamond wheel forms an anode connected to the positive terminal of the rectifier. Grinding of the metal part is achieved by spraying an electrolyte fluid between the diamond wheel and metal part, connecting electrical power from the rectifier to the cathode and anode, and simultaneously rotating the diamond wheel while advancing it across the metal part. With this grinding machine, approximately 10% of metal is removed from the metal part by grinding and 90% removed by electrochemical anodic action.